Gail, I am so sorry ds is dealing with this. i don't have much helpful to add to the above posters. I wouldn't force him to go on the field trip if it's an option for him to stay home and he wants to. Then, yes, time to regroup and huddle up with the adults at school to bring this to their awareness and come up with some plans. Noah might even have some good ideas himself about how to make this rough patch a bit easier for him (I do believe and hope it's just a rough patch and then things will find a new and good normal).
Dd once made a comment sort of like what ds has told you and, yes, it made me cry (not in front of her, of course!) and she was only 3. I can only imagine it would/will be that much harder when she is older and even more aware of all the dynamics at play...
me:smc (single mom by choice)
Dd: Conceived when I was 42 after 2 years ttc. Conceived on 6th IVF cycle after 2 bfn's and 3 m/cs.